Equalized delay line



Feb- 8, 1949- H. E. KALLMANN EQUALIZED DELAY LINE Filed Feb. 7, 1946 (PIC-3.!

FIG. 2

INVENTOR. HEINZ E. KALLMANN ATTORNEY Patented Feb. 8, 1949 EQUALIZED DELAY LINE Heinz E. Kallmann, New York, N. Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application February '7, 1946, Serial No. 546,163

This invention relates to artificial transmission lines and more specifically to artificial trans mission lines of the distributed parameter type compensated for uniform response over a wide range of frequencies.

Artificial transmission lines, called delay lines, are used in high frequency transmission and signalling systems hen it is desired to delay a signal or pulse for a predetermined interval of time. The proper transmission of a pulse through the delay line depends upon the ability of the line to transmit a large range of frequencies with equa1 attenuation and equal time of delay. A delay line of the distributed parameter type is described and illustrated in copending patent application S. N. 496,139, filed July 26, 1943, by Richard B. Nelson, Patent No, 2,420,559, issued May 13, 1947, and entitled Artificial transmission line. In a delay line of this type, the time of delay is proportional to the inductance of the winding and the capacity between the winding and ground. The capacity between the winding and ground is substantially independent of frequency, but the inductance of the winding decreases with increasing frequency. This effect is evidenced in a reduced time of delay for the higher frequencies, causing distortion of the transmitted signal or pulse.

A primary object of the present invention is to provide an improved delay line of the distributed parameter type by compensating for the above mentioned difiiculty.

An additional object is to provide a means for equalizing the time delay of a delay line over the whole video frequency range.

A further object is to provide a compensated delay line providing uniform time delay of signals over the whole video frequency range.

The invention itself, together with the method of operation and advantages thereof may best be understood from the following description when taken with the accompanying drawings, in which:

Fig. 1 shows a view of a delay line embodying this invention; and

Fig. 2 shows a transverse section of the delay line along the line II-II in Fig. 1.

Referring to the accompanying drawing, a delay line of the distributed parameter type is shown. The delay line consists of a helical coil I formed by a conductor H with suitable insulation l2 thereon. The coil lllls wound over a supporting form l3 of substantially cylindrical shape and composed of a suitable dielectric materlal. While coil I0 is shown covering only part 6 Claims. (Cl. 178-44) of the length of form l3 for clarity, it is to be understood that coil lil extends substantially the full length of form 13. Between coil l0 and form 53 is a layer of narrow conducting strips I l. The strips M are parallel to the axis of coil it! and are electrically separated throughout their length, except at the transverse portion l6 where they are brought together and grounded. Also between coil it and form I3 is a series of patches 5. The patches 15 are formed of conducting material electrically separated from the conductor l l, strips I4, and each from the other patches l5.

The terminals of the delay line are formed by the two ends of conductor H and the grounded strips 54. In operation a signal or pulse is applied between one end of conductor H and ground and appears between the other end of conductor H and round at a later time. This difference in time between the applied signal and output signal is called the delay time. The delay time is proportional to the inductance of the coil Ill and the capacity between the conductors ll of coil and the grounded conducting strips Hi. The delay of a signal should depend only upon these two reactive parameters, the inductance and ground capacity per unit length. However, the delay also depends upon the mutual inductance between any two parts of the coil 10. The mutual inductance decreases with increasing frequency, because with increasing frequency the current, and hence the magnetic field of distant, yet magnetically linked turns, becomes more and more out of phase. Thus, the magnetic fields being more out of phase, distant turns contribute less to each others fields. This effect is compensated for by capacitors which bridge the delay line to link distant turns. To provide such linking the patches !5 are capacitively coupled to groups of turns forming the bridging capacitors. As the magnetic fields of the turns bridged by patches l5 become more out of phase with increasing frequency, the effect of the bridging capacity increases. This effect increases until the field of the turns linked become out of phase.

The length of the patches 55 determines the maximum frequency of compensation. The degree of compensation provided depends upon the bridging capacity provided by the patches. The width of the patches, also the thickness and dielectric constaut of the insulation between them and the coiled conductor, serve to control the amount of bridge capacity provided. The desired isochronisrn, or other delay characteristic, can be or the'strips l4 and patches l5 may be formed by a plating of copper or silver on the surface of the form l3. The conductor ll, preferably copper, may be covered with insulation l2 suitable to withstand the voltage for which the line may be used, or the insulation l2 may be enamel having a low voltage rating and a layer of high voltage insulation placed between the coil l0 and the strips M.

It is understood that this invention is not limited to the details of construction illustrated in the accompanying drawing and described above, except as appears hereafter in the claims.

What is claimed is:

1. Compensation for a delay line of the distributed parameter type, said delay line including a helical coil of a conductor and means for providing distributed capacity between said coil and ground, said compensation comprising a plurality of insulatively mounted conducting patches, said patches capacitively coupling a number of turns of said coil of said delay line.

2. A delay line comprising, a helical coil of an insulated conductor surrounding a number of conducting strips parallel to the axis of said coil, said strips being conductively coupled at one point, a plurality of conducting patches insu1atively mounted, said patches being capacitively coupled to said coil.

l .and ground,

3. A delay line comprising, a substantially cylindrical core of insulating material having on its surface a number of conducting strips, said strips being parallel to the axis of said core, and being conductively coupled at one point forming one terminal of said delay line, a conductor, suitably insulated, forming a helical coil surrounding said core and strips, a plurality of conducting patches insulatively mounted and forming capacitive coupling between distant turns of said coil.

4. A delay line of the distributed parameter type comprising, a substantially cylindrical core of insulating material, a plurality of conducting strips on the surface of said core, said strips being substantially parallel to the axis of said core, said strips being insulated except at one point where said strips are conductively coupled, a plurality of conducting patches on the surface of said core, said patches being insulatively mounted, a winding of an insulated conductor forming a helical coil surrounding said core, strips, and patches.

5. A. frequency compensated delay line of the distributed parameter type, said delay line including a helical coil of a conductor, a conductive member disposed in spaced relationship to said coil providing distributed capacitance between said coil and said conductive member, and a plurality of insulatedly mounted conducting patches, said patches capacitively coupling a number of turns of said coil of said delay line.

6. A frequency compensated delay line of the distributed parameter type, said delay lin including a helical coil of a conductor, means providing distributed capacitance between said coil and a plurality of insulatedly mounted conducting patches, said patches capacitivel coupling non-adjacent turns of said coil of said delay line.

HEINZ E. KALLMANN.

No reference cited. 

